The present invention relates generally to security apparatus for information processing systems, and more particularly to apparatus for selectively controlling the deciphering of information signals, such as scrambled television programs.
There are many schemes available for controlling the remote descrambling of television signals. Such schemes are necessary to maintain security in subscription television systems, including cable television systems and satellite television systems. Typically, a system subscriber is provided with a descrambler connected between a television signal source (e.g., cable feed or satellite receiver) and a television set. Each subscriber's descrambler is remotely accessed by the system operator to enable or disable the receipt of specific services such as the Home Box Office movie channel or special pay-per-view sports events. One problem with such systems is that "pirates" are apt to break the system security and sell "black boxes" that enable the reception of all programming without paying for the services received. It has been difficult and expensive for system operators to contend with the piracy problem. Once a particular security system is breached, the system operator must usually replace all existing descramblers with new units that operate with a different security algorithm. This solution is not cost effective.
Various systems have been designed to make piracy more difficult. One such system is disclosed in U.S. Pat. No. 4,613,901 to Gilhousen, et al entitled "Signal Encryption and Distribution System for Controlling Scrambling and Selective Remote Descrambling of Television Signals", incorporated herein by reference. In the Gilhousen, et al system, a "working key" signal is generated in accordance with the well known data encryption standard ("DES") security algorithm, after the algorithm is keyed by either a common category key signal or some other key signal. A unique encryption key stream is generated by processing an initialization vector signal in accordance with the DES algorithm when the algorithm is keyed by the working key signal. A television signal is scrambled in accordance with the unique encryption key stream to provide a scrambled television signal. A plurality of unique encrypted category key signals individually addressed to different selected subscribers' descramblers are generated by processing the initial common category key signal in accordance with the DES algorithm when the algorithm is keyed by a plurality of different "unit key" signals associated with different descramblers. The scrambled television signal, initialization vector signal, and plurality of encrypted category key signals are broadcast to the descramblers. At each descrambler, the encryption key stream is reproduced to descramble the television signal. Each descrambler has its unique unit key signal stored in memory for use in reproducing the common category key signal when the descrambler is addressed by its unique encrypted category key signal. By using the DES algorithm, the Gilhousen, et al system provides a high level of security, making it difficult and expensive for a pirate to reproduce the working key.
Other selective subscription descrambling systems are disclosed in Gilhousen, et al U.S. Pat. Nos. 4,712,238 and 4,792,973. These patents provide improved systems for enabling descrambling of a received scrambled signal on an impulse-purchase basis. U.S. Pat. No. 4,634,808 to Moerder discloses a system for reproducing a key signal in a descrambler that is unique to the descrambler, and was used in encrypting a key signal that must be decrypted for use in descrambling a television signal. However, no security system is unbreakable, and determined pirates can be expected to ultimately prevail.
It would be advantageous to provide an improved system in which security can be economically upgraded after a breach. It would be further advantageous if the security upgrades could be made in the field by the simple replacement of a relatively low cost security element containing a new security algorithm. The security element should be replaceable by a subscriber in his home without any need for a visit from service personnel.
It would also be advantageous to protect the interface between the subscriber's descrambler and the replaceable security element, so that others could not easily manufacture their own security elements to defeat the system or to use the descrambler for other unauthorized purposes. If the wrong security element is installed, the descrambler must not work.
The present invention provides an upgradeable security system, an information processor, and a replaceable security element that enjoy the aforementioned advantages.